Method and apparatus for the injection moulding of articles formed by plastic materials having different characteristics

ABSTRACT

The injection moulding of articles formed by plastic materials having different characteristics, for example of different colours, is carried out in a single injection cycle in which the first and the second plastic materials are injected into a first and into a second zone of a mould cavity by first and second injectors controlled according to specific modes so as to define a shape and/or a position of a weld line.

FIELD OF THE INVENTION

The present invention regards a method and an apparatus for theinjection moulding of articles formed by plastic materials havingdifferent characteristics.

The expression “different characteristics” is used to indicate, in thedescription and in the claims that follow, plastic materials having thesame composition but different colours to obtain articles of two or moredifferent colours, or plastic materials having different compositions soas to obtain—in the same article—aesthetically or structurally differentzones, for example having greater or lesser rigidity, or even bothdifferences.

The invention particularly advantageously applies to the moulding ofcomponents of large dimensions for example in the automotive industry(bumpers, spoilers etc.) in which, for aesthetic and/or structuralreasons, the aforementioned differentiations are required.

STATE OF THE PRIOR ART

As concerns the manufacturing of articles thus made, the conventionalmethod typically provides for the use of rotary moulds between two (ormore) stations for the injection of the two (or more) differentmaterials.

For example, as concerns manufacturing a two-coloured article such as alens of the rear light, the moulding phases initially provide for theinjection of the material of a first colour into a first cavity to formthe first part. The mould is then opened, rotated by 180° and closedagain for the subsequent injection of the second material and theformation of the second part which is joined to the first part.

These moulds are very complex to manufacture and thus expensive, entailrelatively long moulding times and require frequent maintenanceoperations. Furthermore, the weld line between the two (or more) partsof the moulded articles is uniquely and strictly determined and notsusceptible, unless after modifying the mould, to variations that couldpossibly be suitable for improving the aesthetic result of the mouldedarticles.

Document U.S. Pat. No. 5,556,582 describes a system for controlling theinjectors of an injection moulding apparatus in which each injector canbe controlled individually to improve the quality of the moulded piecesusing a single plastic material.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the aforementioneddrawbacks and enable the injection moulding of articles formed byplastic materials having different characteristics, without having touse rotary moulds.

A further object of the invention is to be able to adjust theconfiguration, in terms of shape and position, of the weld line/sbetween the different materials.

According to the invention, this object is attained thanks to a methodfor the injection moulding of articles formed by plastic materialshaving different characteristics, characterised in that it is carriedout in a single injection cycle consisting of:

providing a mould having at least one cavity in which there areidentified at least one first and one second zone placed incommunication with each other and to which there are associatedrespective first and second injectors with controlled opening andclosing respectively supplied with at least one first plastic materialand one second plastic material having said different characteristics,

injecting the first and the second plastic material respectively intothe first and into the second zone of the mould cavity by means of saidfirst and second injectors so as to originate respective flow frontswhose collision generates at least one weld line,

controlling said first and second injectors according to specific modesso as to define the shape and/or the position of said at least one weldline.

The following significant advantages are attained thanks to thissolution idea:

-   -   Manufacturing simplification and small dimensions of the mould,    -   Lower mould designing/production costs,    -   Lower maintenance;    -   Higher productivity;    -   Flexibility of the shape and position of the weld line between        the different injected materials.

As concerns the production of large articles, such as for examplebumpers for motor vehicles, the injection is typically carried out usinga plurality of injectors arranged along the cavity of the mould andcontrolled in a sequential or cascade manner. The moulding cycleprovides for a filling phase in which the injectors are opened accordingto a preset sequence to progressively fill the mould cavity and asubsequent phase for packing the plastic material injected into themould cavity.

The aforementioned said specific modes can be carried out in the fillingphase and/or in the packing phase.

In particular in order to define the position of the weld line, theopening of the at least one injector can be anticipated or delayed withrespect to the other injectors, and in order to define the shape of saidweld line, at least one of the injectors can be opened gradually andonly partially, and at least one of the injectors can be closedpartially.

The invention also regards an apparatus for the injection moulding ofarticles formed by plastic materials having different characteristics,which is configured to carry out the aforementioned method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to anon-limiting example illustrated in the attached drawings, wherein:

FIG. 1 is a partial and schematic perspective view which generally showsthe essential components of an injection moulding apparatus according tothe invention for obtaining a bumper for motor vehicles,

FIG. 2 is a plan view of FIG. 1,

FIG. 3 shows in larger scale the bumper of FIG. 1, and

FIG. 4 shows the enlargement indicated by the arrow IV of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

The following description refers to a specific embodiment of theinvention, in particular regarding the moulding of a bumper for motorvehicles, which shall however not be deemed limiting in any mannerwhatsoever. The invention also applies to the injection moulding ofarticles of any kind and type formed by two or more plastic materialshaving different characteristics in terms of aesthetic aspects, inparticular colour and/or structural properties.

FIG. 1 schematically shows the bumper S, i.e. the mould cavity for theforming thereof, and it entirely generally and essentially represents asequential injection moulding apparatus for the forming thereof. In thisschematisation, the equipment comprises six injection points provided intwo groups of three A, B, C and A′, B′, C′ arranged in proximity of themutually communicating end zones S1, S2 of the mould cavity S.

The injection points A, B, C and A′, B′, C′ consist, in an entirelyconventional manner (for example as described and illustrated in U.S.2015/0266216 on behalf of the Applicant in question) in injectors 1, 2,3 and 4, 5, 6 supplied by two distinct distributors 13, 14 of plasticmaterial for example of two different colours. Each injector 1, 2, 3 and4, 5, 6 comprises—in a conventional manner—a respective nozzle and avalve pin displaceable between a closing position and an openingposition by means of a respective hydraulic, pneumatic or preferablyelectric actuator 7, 8, 9 and 10, 11, 12. The actuators 7-12 arecontrolled by an electronic unit 15, programmable for controlling theposition and displacement speed of the valve pin of each injector 1, 2,3 and 4, 5, 6, or groups of such injectors, between the opening andclosing positions.

The moulding process can typically consist in a sequential injectionwhich provides for a filling phase—simultaneous or at different times—ofthe zones S1, S2 of the mould cavity S, in which the injectors 1, 2, 3and 4, 5, 6 are opened in pre-established sequences for progressivelyintroducing the plastic material into such zones S1, S2, and asubsequent phase for packing the plastic materials thus injected.

During the filling phase, the plastic material of the first colour andthat of the second colour introduced into the mould, originate two flowfronts that advance in opposite directions from the zones S1, S2 towardsthe central zone of the cavity S and whose collision generates the weldline schematised with L in FIGS. 3 and 4, which would be generallyvisible on the moulded piece.

According to the distinctive characteristic of the invention, theelectronic unit 15 is configured for defining, by controlling the motors7-12 and thus the injectors 1-6, the shape and/or the position of theweld line L.

For example, anticipating or delaying the opening of one or more of theinjectors 1, 2, 3 or of the injectors 4, 5, 6 during the filling phase,the weld line L can be displaced on one side, as indicated with L′ inFIG. 4, or on the opposite side in L″. Basically, the weld line can thustranslate parallel to itself for example up to being positioned in anon-aesthetic zone, such as for example a rib of the bumper S. In thiscase, the weld line will basically be invisible from the external.

The shape of the weld line L (or L′ or L″) can also be modified, so asto be curve-shaped instead of straight-shaped for example, if at leastone of the injectors 1, 2, 3 or the injectors 4, 5, 6 is openedgradually and only partially, or if closed partially.

These are clearly only some of the possibilities of modifying theposition and shape of the weld line L, which can be carried out withspecific modes by the control unit 15 both in the filling phase and inthe packing phase.

Obviously, pieces shaped differently from the bumper S may require anumber, a positioning and specific injection modes different from thosedescribed in the example, but however managed for controlling anddefining the shape and/or the position of the or of each weld line onthe moulded piece. In all these cases, positioning and maintaining oneor more injectors in partial opening/closing position will enabledefining the shape of the weld line, and the opening anticipation/delayof one or more of the injectors will enable defining the positioning ofthe weld line.

1.-8. (canceled)
 9. An apparatus for the injection moulding of articlesformed by plastic materials having different characteristics, theapparatus comprising: a mould having at least one cavity having at leastone first and one second zone placed in communication with each otherand to which there are associated respective first and second injectorswith controlled opening and closing, respectively supplied with at leastone first plastic material and at least one second plastic materialhaving said different characteristics, an electronic control unitconfigured to control a position displacement and/or speed of a valvepin of the first and second injectors during a single injection cycleto: inject the at least one first and the second plastic materialsrespectively into said first and into said second zone of the at leastone mould cavity by said first and second injectors so as to originaterespective flow fronts whose collision generates at least one weld line,and control said first and second injectors according to specific modesso as to define a shape and/or a position of said at least one weldline, wherein the opening of at least one injector of the first andsecond injectors is either anticipated or delayed with respect to theother injectors of the first and second injectors so as to define theposition of said at least one weld line, wherein at least one of saidfirst and second injectors is closed partially so as to define the shapeof said at least one weld line, and wherein at least another one of saidfirst and second injectors is opened gradually and only partially so asto define the shape of said at least one weld line. 10.-11. (canceled)12. The apparatus according to claim 9, wherein the single injectioncycle includes a filling phase in which said first and second injectorsare opened by the electronic control unit according to pre-establishedsequences so as to progressively said first and second zones of the atleast one mould cavity with said at least one first and second plasticmaterials, and a subsequent packing phase for packing such plasticmaterials injected into the at least one mould cavity.
 13. The apparatusaccording to claim 12, wherein at least one of said specific modes iscarried out in the filling phase.
 14. The apparatus according to claim12, wherein at least one of said specific modes is carried out in thepacking phase.